Herminda Reinoso

Exogenous Abscisic Acid Increases Carbohydrate Accumulation and Redistribution to the Grains in Wheat Grown Under Field Conditions of Soil Water Restriction

This work investigates the effects of abscisic acid (ABA) on physiologic parameters related to yield in wheat (Triticum aestivum) grown under field conditions with water restriction ranging between 45.7% and 49.5% of field capacity during anthesis and postanthesis. ABA (300 mg L−1) was sprayed onto the plants at the beginning of shoot lengthening which significantly promoted leaf area and higher concentrations of chlorophylls and carotenoids in flag leaf at anthesis. ABA also increased soluble carbohydrates in shoots at anthesis, which were then re-exported to the grains at maturity. This correlated with a yield increase that was achieved by a higher number and weight of grains per spike, but protein content was not significantly affected.

Comparative Study of Alkaline, Saline, and Mixed Saline–Alkaline Stresses with Regard to Their Effects on Growth, Nutrient Accumulation, and Root Morphology of Lotus tenuis

Both saline and alkaline conditions frequently coexist in nature; however, little is known about the effects of alkaline and salt–alkaline stresses on plants. We performed pot experiments with four treatments, control without salt addition and three stress conditions—neutral, alkaline, and mixed salt–alkaline—to determine their effects on growth, nutrient accumulation and root architecture in the glycophytic species Lotus tenuis. Neutral and alkaline salts produced a similar detrimental effect on L. tenuis growth, whereas the effect of their combination was synergistic. Neutral salt addition, alone or mixed with NaHCO3, led to significant leaf Na+ build up and reduced K+ concentration. In contrast, in plants treated with NaHCO3 only, Na+ levels and the Na+/K+ ratio remained relatively unchanged. Proline accumulation was not affected by the high pH in the absence of NaCl, but it was raised by the neutral salt and mixed treatments. The total root length was reduced by the addition of NaCl alone, whereas it was not affected by alkalinity, regardless of the presence of NaCl. The topological trend showed that alkalinity alone or mixed with NaCl turned the root more herringbone compared with control roots, whereas no significant change in this index was observed in the treatment with the neutral salt only. The pattern of morphological changes in L. tenuis root architecture after the alkaline treatment (in the absence of NaCl) was similar to that found in the mixed salt–alkaline treatment and different from that observed in neutral salt. A unique root morphological response to the mixed salt–alkaline stress was the reduction in the ratio between xylem vessels and root cross-sectional areas.

Alternative Mechanism for the Evaluation of Indole-3-Acetic Acid (IAA) Production by Azospirillum brasilense Strains and Its Effects on the Germination and Growth of Maize Seedlings

We evaluated the production of indole-3-acetic acid (IAA) by Azospirillum brasilense strains in vitro (cell culture supernatants) and in vivo (stems and roots of maize seedlings) to clarify the role of this phytohormone as a signaling and effector molecule in the symbiotic interaction between maize and A. brasilense. The three strains all showed IAA production when cultured in NFb medium supplemented with 100 μg/ml L-tryptophan. The level of IAA production was 41.5 μg/ml for Yu62, 12.9 μg/ml for Az39, and 0.15 μg/ml for ipdC-. The release of IAA into culture medium by the bacteria appeared to be the main activator of the early growth promotion observed in the inoculated maize seedlings. The application of supernatants with different IAA contents caused significant differences in the seedling growth. This observation provides the basis for novel technological tools for effective quality control procedures on inoculants. The approach described can be incorporated into different inoculation methods, including line sowing, downspout, and foliar techniques, and increase the sustainability of symbiotic plant-bacteria systems.

Application of abscisic acid promotes yield in field-cultured soybean by enhancing production of carbohydrates and their allocation in seed

This study investigates the effect of abscisic acid (ABA) and gibberellin (GA3) applications on physiological and productive parameters in complementary experiments performed with soybean cultured in the field for 3 crop seasons and in the greenhouse for 1 crop season. ABA 300 mg/L was sprayed at the V7 and R2 phenological stages, while GA3 300 mg/L was sprayed at R2 and repeated 7 days later. GA3-treated plants had longer shoots and ABA-treated plants had greater dry weight of aerial parts. Nodule formation was not affected, but both shoot diameter and root density were greater in ABA-treated plants. ABA increased leaf area and chlorophyll content, while GA3 diminished them. In ABA-treated plants, there was a significant reduction in leaf conductance 24 h after the hormone had been applied, but then the conductance values started to rise and equalled those of the controls 11 days later. Although there were no differences in number of pods, in GA3-treated plants the number of seeds per pod was lower, and in ABA-treated plants, young pods were bigger. ABA application increased soybean yield by enhancing carbon allocation and partitioning to the seed. Exogenous ABA also improved the seed quality since it did not affect protein levels but enhanced oil concentration, while GA3 spraying increased oil concentration but diminished seed proteins.

ABA action on the production and redistribution of field-grown maize carbohydrates in semiarid regions

The aim of this study is to analyze the response of exogenous abscisic acid (ABA) application in plants grown under field conditions in semiarid zones in order to increase maize production. For this, it is necessary to understand the factors, such as the size and capacity of transport system involved in the mobilization and distribution of assimilates. The vascular transport capacity of ABA-treated and control plants was compared in terms of number of vascular bundles, phloem area per bundle, and the proportion of phloem in the ear peduncle of female inflorescences. This study showed that the application of exogenous ABA in field-grown maize under moderate drought allows a greater amount of maize production, an increase in the level of photosynthetic pigments, the carbohydrates remobilization to grain, and the capacity of this transport by an increase in the number of vascular bundles and the phloem area in peduncle. Evidence obtained in this study suggests that ABA could help improve agricultural production in rain-fed crops in which irrigation is not possible. This will allow us to follow a new technological strategy to increase the effective filling of organs during crops in unfavorable water conditions.

Dormancy in peach (Prunus persica L.) flower buds

SummaryPeach buds (floral and vegetative) were periodically collected from midsummer until the spring flowering and sprouted under continuous light, 100% relative humidity and 20–25°C. Treatments with 200 ppm gibberellin A3 (GA3) or chilling (2–4°C for 30 days before planting) were applied. Vegetative buds showed well-defined phenological stages: pre-dormancy, “true dormancy”, and end of dormancy. Both GA3 and chilling treatments shortened the sprouting times of vegetative dormant buds close to those in predormancy. Isolated floral buds were irresponsive under all conditions and did not sprout even with the GA3 or chilling treatments. In a comparative study with buds immediately after collection anatomical analysis demonstrated that vegetative buds were almost completely developed by midsummer/early automn and remained in a resting state until the end of winter. Floral buds developed continuously over the same period. Both types of verticils began to differentiate in midsummer. Sepals and petals developed mainly in late summer, androecious floral parts developed throughout the resting period, while gynoecious floral parts showed differentiation in late winter. The flower was completely formed a few days prior to blossoming. Thus, in isolated peach buds fertile verticils are not sufficiently developed during the resting time to allow sprouting.

ABA and GA3 increase carbon allocation in different organs of grapevine plants by inducing accumulation of non‐structural carbohydrates in leaves, enhancement of phloem area and expression of sugar transporters

Grape quality for winemaking depends on sugar accumulation and metabolism in berries. Abscisic acid (ABA) and gibberellins (GAs) have been reported to control sugar allocation in economically important crops, although the mechanisms involved are still unknown. The present study tested if ABA and gibberellin A3 (GA3) enhance carbon allocation in fruits of grapevines by modifying phloem loading, phloem area and expression of sugar transporters in leaves and berries. Pot-grown Vitis vinifera cv. Malbec plants were sprayed with ABA and GA3 solutions. The amount of soluble sugars in leaves and berries related to photosynthesis were examined at three points of berry growth: pre-veraison, full veraison and post-veraison. Starch levels and amylase activity in leaves, gene expression of sugar transporters in leaves and berries and phloem anatomy were examined at full veraison. Accumulation of glucose and fructose in berries was hastened in ABA-treated plants at the stage of full veraison, which was correlated with enhancement of Vitis vinifera HEXOSE TRANSPORTER 2 (VvHT2) and Vitis vinifera HEXOSE TRANSPORTER 6 (VvHT6) gene expression, increases of phloem area and sucrose content in leaves. On the other hand, GA3 increased the quantity of photoassimilates delivered to the stem thus increasing xylem growth. In conclusion, stimulation of sugar transport by ABA and GA3 to berries and stems, respectively, was due to build-up of non-structural carbohydrates in leaves, modifications in phloem tissue and modulation in gene expression of sugar transporters.

Arsenic stress induces changes in lipid signalling and evokes the stomata closure in soybean

Soybean (Glycine max) is often exposed to high arsenic (As) level in soils or through irrigation with groundwater. In previous studies on As-treated soybean seedlings we showed deleterious effect on growth, structural alterations mainly in root vascular system and induction of antioxidant enzymes. However, there are not reports concerning signal transduction pathways triggered by the metalloid in order to develop adaptive mechanisms. Phosphatidic acid (PA), a key messenger in plants, can be generated via phospholipase D (PLD) or via phospholipase C (PLC) coupled to diacylglycerol kinase (DGK). Thus, changes in PA and in an enzyme involved in its metabolism (PLD) were analysed in soybean seedlings treated with 25 μM AsV or AsIII. The present study demonstrated that As triggers the PA signal by PLD and also via PLC/DGK mainly after 48 h of As treatment. DGPP, other lipid messenger produced by phosphorylation of PA by PAK increased in As treated roots. Arsenic also induced rapid and significant stomatal closure after 1.5 h of treatment, mainly with AsIII, probably as an adaptive response to the metalloid to reduce water loss by transpiration. This report constitute the first evidence that shows the effects of As on lipid signalling events in soybean seedlings which would be crucial in adaptation and survival of soybean seedlings under As stress.

Anatomical, Morphological, and Phytochemical Effects of Inoculation with Plant Growth- Promoting Rhizobacteria on Peppermint (Mentha piperita)

Plant growth-promoting rhizobacteria (PGPR) generally exert their effects through enhancement of plant nutrient status and/or phytohormone production. The effects of PGPR on aromatic plant species are poorly known. We measured plant growth parameters, chlorophyll content, trichome density, stomatal density, and levels of secondary metabolites in peppermint (Mentha piperita) seedlings inoculated with PGPR strains Bacillus subtilis GB03, Pseudomonas fluorescens WCS417r, P. putida SJ04, or a combination of WCS417r + SJ04. The treated plants, in comparison with controls, showed increases in shoot biomass, root biomass, leaf area, node number, trichome density, and stomatal density, and marked qualitative and quantitative changes in monoterpene content. Improved knowledge of the factors that control or affect biosynthesis of secondary metabolites and monoterpene accumulation will lead to strategies for improved cultivation and productivity of aromatic plants and other agricultural crops without the use of chemical fertilizers or pesticides.

Differential effects of sodium salts on the germination of a native halophytic species from South America: Prosopis strombulifera (Lam.) Benth

Prosopis strombulifera is a halophytic shrub frequently found in the salinized areas of central Argentina. Interactions between temperature, ionic and osmotic components of salinity, and seed germination in this species are discussed in this chapter. Besides the osmotic effect, specific ion effects of salts play an important role in seed germination causing toxicity to the embryo. In saline soils where P. strombulifera is frequent, NaCl and Na2SO4 proportions are similar. Germination experiments with both salts, their iso-osmotic anionic and cationic mixtures and polyethylene glycol (PEG) were performed at 30°C and 35°C; the germination percentages registered with PEG were lower than those obtained with iso-osmotic Na-based monosaline solutions at osmotic potential (Ψo) of -1.2 MPa and lower, but greater than those in the salt mixtures, indicating that seeds were mainly affected by an osmotic effect rather than by ionic toxicity at 35°C. The salt mixture accentuated ion toxicity showing that germination is inhibited by a combination of osmotic and ionic effects, the latter having greater influence at very high salt concentrations. The excess of Cl- or SO4 2- anions in both cationic mixtures produced equal magnitude of toxicity on the seeds. Although a deleterious effect of potassium was also observed, the anionic effects were evidently much more marked. From Ψo of -1.2 MPa and lower, germination inhibition increased when salt concentration increased as the ionic effects were additive to osmotic effects. The germination percentages obtained with monosaline solutions at 35°C were superior to those obtained at 30°C, indicating that temperature played an important role in the germination response of this species by diminishing the osmotic effect of salt only in the case of monosaline solutions; however, the toxic effect of ions was accentuated when they were combined. Nevertheless, a partial reversion of sulfate toxicity was observed when seeds were placed in anionic salt mixtures at 30°C, demonstrating the differential effects of temperature on the osmotic and ionic components of salinity.